1. Field of the Invention
The present invention relates to the maintenance of a stable, life-supporting environment for high-risk infants and others and especially to devices, methods and systems which can be used in both a stationary and transport mode such as in hospitals, ambulances and aircraft.
2. Description of the Problem and Prior Art
High-risk newborn infants, particulary those with respiratory disease syndrome or other respiratory problems, demand a stable supportive environment, usually including one that is warm, oxygen rich, draft-free and humidified, to minimize the minimize of the illness on their condition. The maintenance of such an environment during transport of the newborn is difficult at best. Especially in remote areas, high-risk infants must often be transported from a small community hospital over a distance of several hundred miles or more by aircraft or ambulance, or both, to a regional intensive care nursery. In such circumstances the maintenance of a protective, stable supportive environment for the infant is particularly difficult, especially because it is often necessary to begin therapy and medical procedures during transport. The foregoing transport problems and recommended equipment, procedures and principles of transport are discussed in the book Transport of High-Risk Newborn Infants -- Principles, Policies, Equipment, Techniques, published by the Canadian Paedriatrics Society, in 1972. Also see in this regard Chapter 6, "Transportation of the High-Risk Infant", of the book Care of High Risk Neonate, by Klaus and Fanaroff.
Conservation or restoration of the high-risk infant's body heat is vital and a particular problem during transport. Hypothermia is a frequent complication and danger in high-risk newborn infants, and can be fatal. See, for example, "Stabilization and Transport of Severely Ill Infants", by Cunningham and Smith in Vol. 20, No. 2 (May 1973), issue of Pediatric Clinics of North America. Also see in this regard Chapter 13, "The Respiratory Distress Syndrome of the Newborn", by George W. Brumley in the book The Critically Ill Child, by Clement A. Smith.
The importance of maintaining an adequate environmental temperature to prevent harmful heat loss in a newborn, and the consequences of not doing so, are discussed in Chapter 8, "Thermoregulation in the Newborn", by J. W. Scopes, of the book Neonatology -- Pathophysiology and Management of the Newborn, published by J. B. Lippincott Company, and in some of the other aforementioned references. According to studies reported in the above Scopes reference, adequate environmental warmth alone tripled the chances of survival of very small newborn babies. The range of environmental temperature that the newborn can tolerate when naked in an incubator is very narrow and therefore must be controlled precisely. The difficulty of maintaining the requiring environmental temperature increases greatly during transport, required if medical or surgical procedures must be administered.
Not only is it difficult to provide adequate warmth for the newborn, but even more difficult is the determination of the optimal thermal environment for the newborn, particularly one in the high-risk category. This, too, is discussed by Scopes in "Thermoregulation in the Newborn", supra, and by some of the other aforementioned references. A baby, like any physical body, exchanges heat by conduction, convection, evaporation and radiation. Babies in controlled environmental chambers, such as clinical warm air incubators, do not experience appreciable heat loss through conduction because they usually lie on a mattress of low conductivity. The major channels of heat loss in infants at moderate temperatures are through convection and radiation. Scopes teaches that convective heat loss can be reduced by increasing the environmental air temperature and reducing air speed. However, a high environmental air temperature can result in high evaporative heat loss, but this can be counteracted by increasing the relative humidity of the environment and reducing air speed. Radiant heat loss from the infant depends on its presenting surface area and skin temperature as compared with the surface temperature of the receiving surface, usually the inside surface of the incubator canopy, which is usually pervious to thermal radiation. Thus thermal radiation represents a major source of heat loss from a naked infant in an incubator. Scopes suggests as a solution to the problem interposing a second layer of the rigid plastic canopy material between the baby and the outer canopy of the incubator, the inside surface of which will be warmed by the warm air of the incubator, thereby reducing appreciably radiant heat loss from the infant. He also suggests the possibility of using a radiant heat source directed into the incubator to counteract radiant heat loss from the incubator.
It is often necessary for the attending physician to begin therapy and medical procedures during transport in order to aid the high-risk newborn in its struggle to survive. Such procedures may include resuscitation and application of continuous positive airway pressure through endotracheal intubation. Other procedures may include endotracheal suction and intravenous feeding. The infant's body temperature, blood pressure and pulse should be carefully monitored, which requires that wire leads extend from the monitoring equipment to sensor-transducers which are applied directly to the infant. See the discussion of some of these procedures in Chapter 1, "Resuscitation of the Newborn Infant", by Fisher and Behrman from Care of the High Risk Neonate, by Klaus and Fanaroff, and "Respiratory Care of Newborn Infants", by Gregory in Vol. 19, No. 2 (May 1971) of Pediatric Clinics of North America, and some of the previously mentioned references.
Ideally all of the foregoing procedures and others should be performed while the infant's environmental temperature, humidity, atmosphere and circulation remain stable at desired levels, a difficult task at best in a nursery setting, and even more difficult in a transport mode.
No prior known environmental chambers enable the maintenance of a stable supportive environment as aforesaid during infant transport and especially while administering procedures during transport. All known environmental chambers readily capable of transport are inadequate to achieve this ideal. For example, U.S. Pat. No. 3,858,570 discloses an environmental chamber having a domed hood with a built-in radiant heat source. However, such chamber is obviously unsuited, because of the supporting equipment on which its operation depends, for use in transporting an infant by ambulance or aircraft. It also provides no disclosed means for maintaining a controlled environmental temperature, humidity, airflow and air-oxygen mixture in the chamber, particularly during transport and while administering procedures to the infant. Other prior art chambers having some or all of the same inadequacies include those shown in U.S. Pat. Nos. 2,822,803; 3,889,670; 3,786,809; 3,335,713; 3,000,379; 2,776,657; and 2,699,775; German Pat. No. 164,163; and Belgian Pat. No. 510,199.
During the development of my present invention over the past several years, I have made and tested under actual operating conditions using newborn infants, both in the nursery and in ambulances and aircraft, various experimental prototype chambers, methods and systems. Such prototypes often exhibited some but not all of the advantages of the invention as disclosed herein. One such prototype was disclosed in the January, 1974, issue of "Our Temperature, Pulse and Respiration", a publication of the Washoe Medical Center in Reno, Nevada, where I am a practising physician.
In my prior copending patent application Ser. No. 516,119, filed Oct. 18, 1974, entitled "Transport and Life Support System for Infants", now U.S. Pat. No. 4,003,378, I disclose an infant life support hood and tray, the hood of which can be pressurized for maintaining a desired atmospheric pressure within the hood under varying ambient pressure conditions such as during transport by unpressurized aircraft or during ground transport at varying elevations. Such hood is also capable of maintaining a continuous positive airway pressure in the infant indirectly through pressurization of the hood chamber or directly using endotracheal intubation. The hood is constructed of a clear rigid plastic for protection and encloses at least the infant's head, neck and chest. A breathable gas is delivered to the hood chamber through small ports in the top of the hood which also has a small access port with a removable cover through which medical procedures can be administered. An infant is placed within the hood through an endwall opening having a flexible closure which must be bonded to the infant's body to create a pressure seal. Suction and IV tubing and wire leads for physiological monitoring transducers are passed through this opening also.
While satisfactory for its intended purpose, the foregoing prior hood does have drawbacks and is not the optimum infant life support chamber for several reasons. First, placement of the infant in the chamber and then sealing the chamber is too difficult and time consuming, and often an imperfect seal is formed. Second, no satisfactory means is provided for maintaining and circulating a desired life-sustaining atmosphere within the hood Third, no satisfactory means is provided for maintaining a desired environmental and body temperature within the chamber. Fourth, access to the infant for administering procedures is too restricted and difficult. Fifth, visibility to the infant is somewhat impaired by the appurtenances on the top wall of the hood. Sixth, better access for monitoring wire and tubing leads is needed. Seventh, no ready means is provided for x-ray photography of the infant while in the hood. Eighth, the hood is not designed for compatibility with and securement to various stationary and transport platforms, and is not readily adaptable for use as part of an overall integrated stationary or transportable life support system. Ninth, the hood and tray combination does not optimally protect the infant during transport Finally, it has been determined through experience that it may be undesirable under many circumstances to pressurize the hood chamber because of the serious and harmful consequences that can result through improper use or malfuncton of the life-support equipment. transport
Accordingly, there is a distinct need for a transportable environmental chamber capable of transporting a high-risk infant alternatively within the hospital or out of the hospital by aircraft or ambulance while maintaining a protective, stable supportive environment for the infant while at rest and during medical procedures.